Sodoku solving now happens in a thread.
Solver is now multithreaded! :D
Optimized speed of checking column.

Allocation of memory for vector takes a god forsaken long time.
Check only the row and column of the effected cell when trying to fill a cell.
Added limitation of how many steps per thread to do until we give new work to thread.
renamed max_solve_retries for clarity.
Threads not total to core count instead of double.

This is much more reasonable than earlier which was wasting time context switching. Instead, change how much steps to allow for similar effect.
Fix for max amount of steps not over flowing as before.
Fix for get_writable_elements not working earlier.
coordinates struct made smaller and more readable.
New work for thread notification now lists what thread was redone.
increment_cell optimized a smidgen.
Partial count solve fixed to actually fill the correct amount of cells.
First thread now gets checked if found a solution.

I have no friggen clue how on earth I missed this earlier.
Compilation on linux now works!
Performance increased sufficiently to re-enable large sodoku test.
Added comments to header usage
Added new tasks to notes.
Revert "Performance increased sufficiently to re-enable large sodoku test."

This reverts commit 9f53e3047ef3c6c71798d755b4c1c8bec439041f.
Cleanup of project description.